[Popliteal cysts: sonography evaluation after arthroscopic treatment]

To identify a set of sonomorphological parameters to evaluate the outcome of arthroscopic surgery for popliteal cysts by sonography.

We examined 30 patients (18 males, 12 females) before treatment and 3/6 months after arthroscopy. Patients were classified by clinical (4 groups) and sonographic criteria. The sonographic criteria were the morphological classification of the cysts (beak-shaped, X-shaped, grape-like, slit-shaped) and the volume measurement.

Sonography identified beak-shaped popliteal cysts (the most frequent Baker cyst shape), 5 grape-like (the usual shape of complicated Baker cysts) and 1 X-shaped . The volume of cysts before treatment ranged from 5 to 38 cl. Most cysts were clinically rated as grade 2 (symptomatic and evident at physical examination, with a reduction of range of motion up to 20 degrees of flexion). No patient was rated as grade 0 (normal). After surgery the cyst was still evident at sonography. After 3 months we recorred a cyst volume decrease in all cases. Six months after surgery 29/30 cysts had a volume <5 cl with an almost virtual cavity that changed their appearance in to slit-shaped . In one case cyst volume increased. The clinical classification showed an increase of the grade 0 group unsymptomatic cysts (not detectable at physical examination).

Sonographic evaluation of popliteal cysts after arthroscopic surgical treatment allowed to recognize the cysts, which are not removed by this approach. The follow-up at 3 months showed a reduction in cyst volume. After six months, in the cases with a good surgical response, the cysts reached a volume <5 cl regardless of their original volume. The morphology of the cysts with a good surgical result, is slit-shaped with virtual cavity regardless of their original appearance. There is a high correlation between sonographic and clinical data. We believe that the volume reduction of the cyst three months after surgery is a good predictive element. After six months the preesence of a cyst with a volume <5 cl and a slit-shape with virtual cavity is a sign of good surgical result.